Method of making a water filter

ABSTRACT

A double shell filter including an inner shell of bounded 80 to 400 U.S. mesh screen carbon particles and an outer shell of bonded 20 to 80 mesh screen carbon particles wherein the inner and outer particles are bonded internally to each other and the two shells are bonded together preferably by an ultra high molecular weight polymer binder having a melt index of less than about 1 gram per ten minutes as determined by ASTM D1238 at 190 degrees C. and 15 kilograms load.

This is a division of Application Ser. No. 849,167; filed Apr. 7,1986,now U.S. Pat. No. 4,753,728.

BACKGROUND OF THE INVENTION

The present invention relates to water filters. Typically, such filterscomprise a hollow core cylindrical block of bonded, activated charcoal.Water flows through the perimeter of the charcoal filter and into thecenter core from whence it flows to the user. Typically, some type ofporous plastic sleeve is located in the core to keep the charcoal fromflaking off into the water.

One problem with such filters is that if the charcoal particles are fineenough to do a proper filtering job, they inhibit water flowsubstantially. One prior artisan has attempted to overcome this bycutting longitudinal grooves in the outer peripheral surface of thefilter. However, it is believed that this merely causes water to flowthrough the filter at the base of the groove and effectively orsubstantially eliminates water flowing through an outer layer of thefilter.

Another problem with bonded charcoal particle filters is that theplastic binder used to bond the charcoal particles together tends toclog the pores of the activated charcoal. While such clogging does notcompletely eliminate the effectiveness of the activated charcoal, itdoes tend to reduce its efficiency.

U.S. Pat. No. 3,950,251 discloses a cylindrical filter element formed ofa polymer bonded, compressed charcoal inner core with a porosity ofabout 10 microns and a second outer filter element sleeve made up ofunbonded granular activated charcoal of 14 to 40 mesh particle size. Aserious problem with such an arrangement is that the outer sleeve ofunbonded charcoal has to be contained in a porous plastic container tokeep the charcoal from spilling out of the filter during shipping andstorage.

Also, water tends to "channel" through the unbonded outer charcoalwithout being filtered. On the other hand, bonding can substantiallylimit the effective surface area of the larger particles, in that thebinder clogs the pores. The effective surface area of the largerparticles is already less per unit of weight than that of the smallerinner particles, and the binder aggravates the problem.

SUMMARY OF THE INVENTION

In the present invention, a satisfactory degree of filtration withoutundue inhibition of water flow is achieved by providing a cylindricalfilter having an inner bonded 80 to 400 U.S. Mesh screen carbon particleshell, most preferably 80 to 325 U.S. mesh screen, and an outer shell ofbonded 20 to 80 U.S. mesh screen and preferably 20 to 60 U.S. meshscreen carbon particles, which is also bonded to the inner charcoalshell so as to create an integral package. This filter is made inaccordance with a unique process whereby a separator sleeve is placedinto a filter mold, a mixture of the smaller carbon particles and binderis placed on the inside of the separator sleeve and a mixture of thelarger charcoal particles and binder is placed on the outside of theseparator sleeve. The separator sleeve is then removed and the mass issintered and pressed to create a unitary carbon filter having twodifferent particle size, integrally bonded layers.

In another aspect of the invention, the carbon particles are bondedtogether by means of a very low melt index polymer, which becomes tackywithout becoming sufficiently liquid to substantially wet the carbonparticle surface. Deleterious diminution of the effective carbon surfacearea is minimized. Further, this unique polymer binder, not heretoforesuggested for use as such, facilitates binding layered masses of carbonparticles, e.g. a two layer system, in that heating sufficiently totackify and bond the innermost layer of particles can be achievedwithout wetting thoroughly the outer layer of particles.

These and other objects, advantages and features of the presentinvention will be more fully understood and appreciated by reference tothe written specification and appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross sectional view of a charcoal filter made inaccordance with the preferred embodiment of this invention; and

FIG. 2 is a perspective partially broken view showing the apparatus formaking the filter.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the preferred embodiment, the filter 1 of the present inventioncomprises an inner porous plastic cylinder 10, an inner bonded carbonsleeve 20 around cylinder 10, an outer bonded carbon sleeve 30, a bottomend cap 40 and a top end cap 50 (FIG. 1). The outer charcoal layer 30 iscovered by fabric 60 and fabric scrim 61, which are held in place byplastic net wrap 70.

Inner plastic sleeve 10 is a conventional porous plastic sleeve whichallows water to flow readily through its cylindrical wall. It isthreaded at one end 11 whereby the filter assembly 1 can be threadedonto a threaded member in a suitable filter housing. It has an outerdiameter such that it fits snugly within inner carbon layer 20. It isfrom 3/4to 1-1/4inch in diameter, and most preferably about 1 inch.

Inner carbon layer or sleeve 20 comprises 80 to 400 mesh U.S. Seriesscreen powdered carbon, and most preferably 80 to 325 mesh powderedcarbon. Activated carbons are produced and identified according to theirmesh size. In an 80 to 325 mesh carbon, the particles are of a size suchthat 90 to 95 percent of the carbon will pass through an 80 mesh screenbut remain on a 325 mesh screen. In contrast, 75 to 85 percent of an 80to 400 mesh carbon will remain on a 325 mesh screen. All screen numbersused herein refer to U.S. Sieve series screens.

In many charcoals, screen size definition is somewhat difficult due tothe presence of "fines." Such fines are extremely fine particles whichwill pass through any practical screen. These may comprise as much as20% by weight of the charcoal and are disregarded by the charcoalproducers themselves in grading their charcoals. The screen gradingreferred to herein also disregards the presence of fines.

Examples of commercially available 80 to 400 mesh carbon include:

    ______________________________________                                        Barnebey Cheney ™ 1003                                                                            YF                                                     Calgon ™            ADP                                                    Calgon ™            GW                                                     Calgon ™            PCBG                                                   Calgon ™            PCB                                                    Calgon ™            RB                                                     Darco ™             S51                                                    Darco ™             S51 FF (fines                                                                 removed)                                               ______________________________________                                    

Commercial examples of the more preferred 80 to 325 mesh carbon includethe following:

    ______________________________________                                        Calgon ™              TOGC                                                 Witcarb ™             950                                                  Barnebey Cheney ™     1006                                                 Calgon ™              TOG                                                  ______________________________________                                    

Of these, Calgon™ TOG is the most preferred.

Inner carbon cylinder 20 extends from the exterior of inner cylindricalsleeve 10 outwardly to an outside diameter of from about 3 to 4 inches,with 3-1/2 inches being preferred. When bonded and pressed as describedbelow, inner carbon layer 20 has a porosity of about .2 microns.

Outer carbon cylinder 30 begins at the exterior of inner cylinder 20 andextends outwardly to an outside diameter from about 4 to about 5 inches,with 4-3/8 inches being preferred. Outer carbon cylinder 30 is comprisedof 20 to 80 mesh carbon, and most preferably 20 to 60 mesh carbon.Examples of commercially available carbon within this range include:

    ______________________________________                                        Calgon ™  TOGX      (20 to 50 mesh screen)                                 Darco ™   SG        (20 by 60)                                             ______________________________________                                    

The preferred binder in accordance with the present invention comprisesa polymeric material with a very low melt index (melt flow rate) whichbecomes tacky at elevated temperatures without becoming sufficientlyliquid to significantly wet the carbon particle surface. The melt flowrate or melt index as determined by ASTM D1238 or DIN 53735 at 190degrees C. and 15 kilograms. load should be less than about 1 gram/10minutes, more preferably less than 0.5 grams/10 minutes and mostpreferably less than 0.1 gram/10 minutes. A most preferred binder is anultra high molecular weight, high density polyethylene. The highmolecular weight gives rise to the restricted flow properties of themelted material which is so important to this aspect of the invention.An example of a commercially available ultra high molecular weight, highdensity polyethylene is Hostalen ®GUR-212. It has a density of 0.935grams per cubic centimeter and a melt index of less than 0.1 grams perten minutes as determined by DIN 53735 at 190/15. Such polyethyleneshave a molecular weight of from about 4 to about 6 million. They have avicat softening point of approximately 74 degrees centigrade and acrystalline melting range of 135 to 138 degrees C.

The temperature at which the most preferred binder becomes sufficientlytacky to adhere to the carbon particles may vary depending on thespecific polymer used. With the high molecular weight, high densitypolyethylene, we find that the binder and carbon particles can beprocessed at a temperature of from about 175 degrees C. to about 205degrees C. for about 2 hours.

The percentage of the preferred binder used to bind the inner layer isfrom about 17 to about 25 percent, and most preferably about 20 percentby weight based on the combined weight of the carbon and binder. For theouter layer, from about 20 to about 30 percent by weight binder is usedin the binder/carbon composition, and most preferably about 25 percent.One must use enough binder to hold the carbon particles together, butavoid using so much as to block the surface pores of the carbonparticles.

The binder must be utilized in powder form so that it can be uniformlymixed and dispersed with the carbon particles. The use of the preferredembodiment polymer binder allows one to bind the carbon particlestogether in both layers without excessively wetting the carbon particleswhen melted and thereby effectively occluding much of the surface areaof the carbon particles. The preferability of using an ultra highmolecular weight, low melt index polymeric material to a conventionalpolymeric binder is established by reference to Table I, containingexamples 1 through 18, below. As can be seen by reference to Table I,the percentage of available carbon is 50 to 100 percent greater or morethan when conventional polymer binders are used.

Of course, as regards that aspect of the present invention which broadlyinvolves using carbon particles of two different size ranges,conventional binders can be employed. These are typically polyethyleneshaving much higher melt indexes. The percentage of binder used tends torun higher in these formulations, e.g., as high as 35 percent. Suchbinders are usually polyethylene or polyethylene copolymer materialshaving molecular weights substantially lower than 4 to 6 million.

The process for making the assembly comprising inner sleeve 10, innercarbon cylinder 20 and outer carbon cylinder 30 involves the use of ahinged cylindrical shaped molding cup 100 having an upwardly projectingcentral dowel 110 (FIG. 2). A separator sleeve 120 is placed in mold 100and is located in a groove 111 in the bottom 101 of mold cup 100.Separator sleeve 120 is approximately 1/8 of an inch thick and can bemade of paper, glass, metal or any other like material.

Once separator sleeve 120 is in place, the inner layer carbon is blendedwith binder and loaded into the space between inner sleeve 10 andseparator 120. A special funnel having a mass flow hopper is used inorder to keep the carbon particles from separating during the fillingoperation. Such funnels have sides sloped at 80 degrees, rather than theusual 60 degrees.

Hinged half 100 of mold cup 100 is closed on half 100 b and the twohalves clamped together by suitable clamping means (not shown). (It isnot essential that mold 100 be hinged, and in production it will not behinged). Then, the outer layer carbon is blended with binder and loadedinto the space between separator sleeve 120 and the outer cylindricalwall of mold cup 100.

With all of the carbon and binder blend in place, separator sleeve 120is removed from mold cup 100. Mold cup 100 and its contents are thenheated to from about 175 to about 205 degrees centigrade.Simultaneously, the carbon/binder blends are subjected to from about 30to about 120 p.s.i. pressure via pressure piston 130 which is loweredinto mold cup 100 and which includes a central clearance opening 131 forinner dowel 110.

Compression piston 130 has approximately the diameter of inner charcoalcylinder 20. This is because compression is required primarily for thesmaller inner carbon particles and binder. If piston 130 were thediameter of both layers 20 and 30 combined, inner layer 20 would notcompress adequately. While some of the outer charcoal particles andbinder get forced up around the outside of piston 130 duringcompression, the "sleeve" thus formed is trimmed off during the latertrim operation.

The carbon/binder layers are then allowed to cool and the compositestructure is removed from mold 100. The binder creates an integratedstructure in which the inner carbon layer 20 is bonded to itself, outercarbon layer 30 is bonded to itself, and both layers are bonded to eachother, thereby creating a unitized structure.

This composite is then trimmed at both ends to create smooth, firm ends.Porous plastic sleeve 10 is inserted into the inner cylinder in innerlayer 20 left by dowel 110. The composite filter is then dipped intomelted polyproplene in a slush mold to form bottom cap 40 (FIG. 1). Topcap 50 is formed in the same way, except that the top cap slush moldincludes a threaded member onto which the threaded end 11 of innerplastic sleeve 10 is threaded so that polyproplene forms around the topend 11 of sleeve 10 and does not get into it and block it as is the casewith bottom cap 40.

The resulting composite is then wrapped with a layer of nonwoven scrim61 and a somewhat thicker nonwoven fabric having an effective porosityof 25-35 microns and a thickness of about 1/8 of an inch. These layersare held in place by a final plastic net 70 which is wrapped aroundfabric 60 as is conventional.

EXAMPLES

The desirability of using a high molecular weight, low melt indexpolymer as a binder is illustrated in examples 1 through 18 reported inTable I. In each example, a filter block was made using the indicatedcarbon and the indicated binder at the indicated percentage. The degreeto which carbon is available in each case to absorb impurities isindicated in the column labeled "percent available carbon". This wasdetermined by comparing the iodine number for the raw carbon to theiodine number for the bound carbon. The melt index for the binders isindicated in the fourth column.

The iodine number is a number expressing the quantity of iodine absorbedby a substance. The sixth column in Table 1 expresses the iodine numberfor the raw carbon. The seventh column expresses the iodine number forthe carbon in its bound form, i.e. in a filter blcok. In each case, thefilter block was first produced in accordance with the process describedabove, and then a portion thereof was ground up for purposes ofdetermining its iodine number. Conventional sodium thiosulfate titrationtechniques were used to determine the iodine number in each case. Thepercentage of available carbon is the bound carbon iodine number dividedby the raw carbon iodine number multiplied by 100.

                                      TABLE I                                     __________________________________________________________________________                                         Bound                                    Ex-                 Melt Index                                                                          %   Raw Carbon                                                                           Carbon                                                                              % Avail                            ample                                                                             Carbon Binder   g/10 min                                                                            Binder                                                                            Iodine No.                                                                           Iodine No.                                                                          Carbon                             __________________________________________________________________________    1   Barnebey ™                                                                        Micro-   5     25% 850    450   53%                                    1003   thene ™ FN510                                                   2   Barnebey ™                                                                        GUR212   <.1   40% 850    654   77%                                    1003                                                                      3   Barnebey ™                                                                        Micro-   5     20% 1050   390   37%                                    YF     thene ™ FN510                                                   4   Barnebey ™                                                                        GUR212   <.1   20% 1050   805   77%                                    YF                                                                        5   Witcarb ™                                                                         Micro-   5     35% 1210   713   59%                                    950    thene ™ FN510                                                   6   Witcarb ™                                                                         GUR212   <.1   35% 1210   1108  92%                                    950                                                                       7   Darco ™                                                                           Polyslip ™                                                                          *     35% 600    100   17%                                    S51    101                                                                8   Darco ™                                                                           Polyslip ™                                                                          *     35% 600    100   17%                                    S51    105                                                                9   Darco ™                                                                           Hercoflat ™                                                                         *     35% 600    297   50%                                    S51    135                                                                10  Darco ™                                                                           Micro-   *     35% 600    187   31%                                    S51    thene ™ FA113                                                   11  Darco ™                                                                           GUR212   <.1   35% 600    413   69%                                    S51                                                                       12  Witcarb ™                                                                         GUR212   <.1   20% 1000   1042  104%                                   940                                                                       13  Witcarb ™                                                                         GUR212   <.1   20% 1000   961   96%                                    940                                                                       14  Witcarb ™                                                                         GUR212   <.1   20% 1000   862   86%                                    940                                                                       15  Witcarb ™                                                                         GUR212   <.1   35% 1210   1000  83%                                    950                                                                       16  Witcarb ™                                                                         GUR212   <.1   35% 1210   1108  92%                                    950                                                                       17  Witcarb ™                                                                         GUR212   <.1   20% 1210   1084  90%                                    950                                                                       18  Witcarb ™                                                                         GUR212   <.1   20% 1210   1060  88%                                    950                                                                       __________________________________________________________________________     *Precise melt index not known, but in each case it was relatively high an     certainly greater than 1 gram/10 minutes.                                

Naturally, the raw carbon iodine number is different for each type ofcharcoal. However in each and every case, the percentage of availablecarbon is substantially greater where the binder used is an ultra highmolecular weight, low melt index polymer. The uItra high molecularweight, low melt index polymer used in examples 2, 4, 6, 11 and 12-18was the Hostalen™ GUR212 discussed above. The other materials areConventional polymer binders of the type typically used to bind carbonparticles in water purifiers and the like or for other purposess.

The filter blocks of examples 1 and 2 are both made using a BarnebeyCheney® carbon, No. 1003. In example 1 wherein 25% of a conventionalpolyethylene binder was used, the percent available carbon was only 53%.When 40% of an ultra high molecular weight, low melt index polymer wasused, the available carbon was 77%. Hence, the available carbon was 50%greater, even though the percentage of binder used was over 50% greater.

In examples 3 and 4, yet another carbon was used. The conventionalbinder at 20% resulted in 37% available carbon, while the preferredembodiment binder at 20% yielded 77% available carbon. Similar resultsare obtained in examples 5 and 6.

In examples 7-11, yet another type of carbon is used. In examples 7-10,a wider variety of conventional polymer binders is employed. The percentavailable carbon varies from 17% to 50%. When the same carbon materialis used with an ultra high molecular weight in example 11, low meltindex polymer, the available carbon is 69%.

Examples 12-18 illustrate that the superior results obtained using anultra high molecular weight, low melt index polymer as a binder arereliably repeatably obtained. In example 12, the results suggest thatthe available carbon actually increases. While this may indicate sometype of synergistic result, it may also be the result of routineexperimental variation and simply a reflection of the fact that a veryhigh percentage available carbon can be obtained using an ultra highmolecular weight, low melt index binder.

Table II includes examples 19-24 which illustrate the superior flow rateobtained using a twin shell construction in accordance with the presentinvention. The carbons used for the inner and outer (if any) filterlayers are indicated, as are the percent binders for the respectivelayers. Flow rate is indicated next. The effectiveness of the filter isreflected in the column headed "Percent Removal Rated Life." The ratedlife of the filter is 500 gallons. The impurity used is chloroform at alevel of 250 parts per billion. The percent removal figure indicates thepercentage of added chloroform which was removed from the 500 gallons ofwater after it had passed through the filter. The hardness of eachfilter was determined using a penetrometer with a 150 gram load. Thefigure indicated is the depth of penetration of the needle in tenths ofmillimeters. In each case, the hardness of the filter block isacceptable.

                                      TABLE II                                    __________________________________________________________________________                    Binder Binder                                                 Ex- Carbon Inner                                                                          Carbon                                                                            Inner  Outer  Flow                                                                             % Removal                                                                           Hard-                                  ample                                                                             Or Single                                                                             Outer                                                                             & %    & %    Rate                                                                             Rated Life                                                                          ness                                   __________________________________________________________________________    19  TOG     --  20% GUR212                                                                           --     .6 97    14.8                                   20  TOG     --  25% GUR212                                                                           --     .7 99    13.5                                   21  TOG     --  20% GUR212                                                                           --     .8 98    17.5                                   22  TOG     TOGX                                                                              20% GUR212                                                                           25% GUR212                                                                           1.0                                                                              99    17.0                                   23  Darco ™ S51                                                                        --  35% Micro-                                                                           --     .76                                                                              No Data                                                                             11.7                                                   thene FN510                                                   24  Darco ™ S51                                                                        SG  35% Micro-                                                                           25% Micro-                                                                           .83                                                                              No Data                                                                             13                                                     thene ™                                                                           thene ™                                                             FN510  FN510                                                  __________________________________________________________________________

In examples 19-21, a filter is made using a single shell of Calgon™ TOGcarbon. That carbon has a particle size distribution of 80 to 325 mesh.An ultra high molecular weight, low melt index polymer was used as abinder. The water flow rate reported is 0.6, 0.7, and 0.8 gallons perminute respectively for each of the examples 19-21.

As can be seen by comparing example 22 to examples 19-21, significantlyimproved flow rate can be obtained by using a twin shell construction inaccordance with the present invention. The outer shell used in example22 is made of Calgon® TOGX, a 20 to 50 mesh carbon material. Thepreferred ultra high molecular weight, low melt index polymer of thepresent invention was used as a binder for both the inner and outercarbon layers. The flow rate of the filter block increased to one gallonper minute as distinguished from 0.6 to 0.8 gallons per minute. Yet, thepercent removal over the rated life of the filter block did not sufferand the hardness was still acceptable.

In examples 23 and 24, a filter block made using only a layer of Darco®S51, an 80 to 400 mesh carbon material, was compared to a filter blockmade using an inner layer of the same carbon and an outer layer ofDarco® SG, a 20 to 60 mesh carbon. The binder used in examples 23 and 24was not the preferred ultra high molecular weight, low melt indexbinder, but rather a conventional polyethylene binder sold commerciallyunder the trademark MICROTHENE® FN510. MICROTHENE® FN510 is apolyethylene binder having a density of0.924 and a melt index of fivegrams per ten minutes as determined by ASTM D 1238. It has a vicatsoftening temperature of 97 degrees C.

In example 23 where only a single shell of bound carbon is used, theflow rate is only 0.76 gallons per minute. By using the twin shellapproach of the present invention (example 24), the flow rate wasincreased to .83 gallons per minute.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows.
 1. A method of making acomposite charcoal filter having inner and outer shells of two differenttypes of charcoal particles comprising:providing a mold defining theexterior configuration of said composite filter; placing a separator insaid composite mold at the desired juncture between said inner and outershells; mixing said inner shell carbon material with a binder andfilling it into said mold to the inside of said separator; mixing saidouter shell carbon material with said binder and filling it into thespace to the outside of said separator, said binder comprising a lowmelt index polymeric material having a sufficiently low melt index thatit will tackify at elevated temperatures without becoming sufficientlyliquid to substantially wet the carbon particles in order thatdiminution of the effective caron surface is minimized; and removingsaid separator and subjecting said two different carbon materials andtheir binders to heat and pressure to cause said carbon particles tobind to each other and to cause said inner shell of carbon material tobond to said outer shell of carbon material whereby an integralcomposite filter can be obtained, wherein said heat and pressure areapplied such that said binder does not become sufficiently liquid tosubstantially wet the carbon particles in order that diminution of theeffective carbon surface is minimized.
 2. The method of claim 1 in whichsaid binder has a melt index of less than 1 gram per ten minutes asdetermined by ASTM D 1238 at 190 degrees C. and 15 kilograms.
 3. Themethod of claim 2 in which said melt index is less than 0.5 grams perten minutes.
 4. The method of claim 3 in which said melt index is lessthan 0.1 gram per ten minutes.
 5. The method of claim 4 in which saidpolymeric binder comprises an ultra high molecular weight polymer havinga molecular weight of from about 4 to about 6 million.
 6. The method ofclaim 5 in which said binder comprises polyethylene.
 7. The method ofclaim 2 in which said polymeric binder comprises an ultra high molecularweight polymer having a molecular weight of from about 4 to about 6million.
 8. The method of claim 7 in which said binder comprisespolyethylene.
 9. The method of claim 1 in which said polymeric bindercomprises an ultra high molecular weight polymer having a molecularweight of from about 4 to about 6 million.
 10. The method of claim 9 inwhich said binder comprises polyethylene.
 11. The method of claim 1 inwhich said carbon particles are subjected to heat at a temperature offrom about 175 degrees C. to about 205 degrees C. and a pressure of fromabout 30 to about 120 pounds per square inch.
 12. The method of claim 1in which said inner carbon material comprises from about 80 to about 400U.S. mesh screen carbon particles and said outer carbon materialcomprises from about 20 to about 80 U.S. mesh screen carbon particles.13. The method of claim 11 in which said binder is a low melt indexpolymeric material having a sufficiently low melt index that it willtackify at elevated temperatures without becoming sufficiently liquid tosubstantially wet the carbon particles.
 14. The method of claim 13 inwhich said binder has a melt index of less than 1 gram per ten minutesas determined by ASTM D 1238 at 190 degrees C. and 15 kilograms.
 15. Themethod of claim 14 in which said melt index is less than 0.5 grams perten minutes.
 16. The method of claim 15 in which said melt index is lessthan 0.1 gram per ten minutes.
 17. The method of claim 16 in which saidbinder comprises polyethylene.
 18. The method of claim 5 in which saidpolymeric binder comprises an ultra high molecular weight polymer havinga molecular weight of from about 4 to about 6 million.
 19. The method ofclaim 18 in which said binder comprises polyethylene.
 20. The method ofclaim 16 in which said polymeric binder comprises an ultra highmolecular weight polymer having a molecular weight of from about 4 toabout 6 million
 21. The method of claim 20 in which said bindercomprises polyethylene.
 22. A method of making a composite charcoalfilter having inner and outer shells of two different types of charcoalparticles comprising:providing a mold defining the exteriorconfiguration of said composite filter; placing a separator in saidcomposite mold at the desired juncture between said inner and outershells; mixing said inner shell carbon material with a binder andfilling it into said mold to the inside of said separator; mixing saidouter shell carbon material with said binder and filling it into thespace to the outside of said separator, wherein said inner carbonmaterial comprises from about 80 to about 400 U.S. mesh screen carbonparticles and said outer carbon material comprises from about 20 toabout 80 U.S. mesh screen carbon particles; and removing said separatorand subjecting said two different carbon materials and their binders toheat and pressure to cause said carbon particles to bind to each otherand to cause said inner shell of carbon material to bond to said outershell of carbon material whereby an integral composite filter can beobtained, wherein said binder comprises an ultra high molecular weightpolymer having a molecular weight of from about 4 to about 6 million,wherein said binder comprises polyethylene; and said carbon particlesused to make said inner shell are finer than those used to make saidouter shell and in which said pressure is exerted on said carbonmaterials and their binders by means of a piston having a diameterapproximately equal to the diameter of said inner shell of carbonmaterial, whereby pressure in concentrsated on said inner shell.
 23. Amethod of making a composite charcoal filter having inner and outershells of two different types of charcoal particles comprising:providinga mold defining the exterior configuration of said composite filter;placing a separator in said composite mold at the desired juncturebetween said inner and outer shells; mixing said inner shell carbonmaterial with a binder and filling it into said mold to the inside ofsaid separator; mixing said outer shell carbon material with said binderand filling it into the space to the outside of said separator, saidbinder comprising a low melt index polymeric material having asufficiently low melt index that it will tackify at elevatedtemperatures without becoming sufficiently liquid to substantially wetthe carbon particles; and removing said separator and subjecting saidtwo different carbon materials and their binders to heat and pressure tocause said carbon particles to bind to each other and to cause saidinner shell of carbon material to bond to said outer shell of carbonmaterial whereby an integral composite filter can be obtained, whereinsaid carbon particles used to make said inner shell are finer than thoseused to make said outer shell and in which said pressure is exerted onsaid carbon materials and their binders by means of a piston having adiameter approximately equal to the diameter of said inner shell ofcarbon material, whereby pressure is concentrated on said inner shell.24. The method of claim 23, in which said binder has a melt index ofless than 1 gram per ten minutes as determined by ASTM D 1238 at 190degrees C. and 15 kilograms.
 25. The method of claim 22 in which saidbinder is a low melt index polymeric material having a sufficiently lowmelt index that it will tackify at elevated temperatures withoutbecoming sufficiently liquid to substantially wet the carbon particles.26. The method of claim 25 in which said binder has a melt index of lessthan 1 gram per ten minutes as determined by ASTM D 1238 at 190 degreesC. and 15 kilograms.
 27. The method of claim 26 in which said melt indexis less than 0.5 grams per ten minutes
 28. The method of claim 27 inwhich said melt index is less than 0.1 gram per ten minutes.
 29. Themethod of claim 23 in which said polymeric binder comprises an ultrahigh molecular weight polymer having a molecular weight of from about 4to about 6 million.
 30. The method of claim 23 in which said bindercomprises polyethylene.
 31. The method of claim 22 in which said carbonparticles are subjected to heat at a temperature of from about 175degrees C. to about 205 degrees C. and a pressure of from about 30 toabout 120 pounds per square inch.
 32. The method of claim 23 in whichsaid carbon particles are subjected to heat at a temperature of fromabout 175 degrees C. to about 205 to about 205 degrees C. and a pressureof from about 30 to about 120 pounds per square inch.